The Redbay Ambrosia Beetle and Laurel Wilt Fungus

Threat to Avocado Trees in Florida

Jonathan H. Crane, Tropical

Fruit Crop Specialist

University of Florida, IFAS

Tropical Research and Education Center

Homestead, FL

Acknowledgements

• J. Johnson, Georgia Forestry Commission, Dry Branch, GA.

• Albert E. Mayfield III, Florida Department Agriculture and Consumer Services, Florida Division of Forestry.

• J.E. Peña, Univ. of Fla., IFAS, Tropical Research and Education Center.

• R.C. Ploetz, Univ. of Fla., IFAS, Tropical Research and Education Center.

• J. Smith, Assistant Professor, IFAS, Department of Forestry and Conservation, Gainesville, Florida

• M. C. Thomas, Florida Department Agriculture and Consumer Services, Department of Plant Industry.

Redbay Ambrosia Beetle and Laurel Wilt Fungus

• There are 38 species of ambrosia beetle in the U.S., 20 of which are non-native.

• There are at least 20 species of ambrosia beetle in Florida.

• Of the 20 or more ambrosia species in Florida, several Xylosandrus sp. attack avocado trees but their boring and their associated fungi do not generally cause the entire tree to die.

• In contrast, the redbay ambrosia beetle and its associated fungus (the laurel wilt fungus; Raffaelea laurelensis) can cause whole tree death.

• The redbay ambrosia beetle appears to be most attracted to woody plants in the Lauraceae (laurel family).

• The native redbay (Persea bobornia), sassafras (Sassafras albidum), and pondspice (Litsea aestivalis) have already been attacked.

• There are over 100 species in the Lauraceae in Florida.– some of these are forest species– some of ornamental value– and one, avocado is a major commercial and door yard fruit crop

species. • The native redbay is in danger of extinction in some

areas of the southeastern U.S. because of the redbay ambrosia beetle-laurel wilt fungus infestation.

Redbay Ambrosia Beetle and Laurel Wilt Fungus

The Redbay ambrosia beetle (Xyleborus glabratus) (Coleoptera: Scolytidae)

• Is in the Tribe Xyleborini• Is a very small (about 2

mm in length), brown-black colored, cylinder-shaped beetle similar to other ambrosia beetles found in Florida.

• The male beetles are smaller than the females and cannot fly. In contrast, the females are strong flyers.

Photographs courtesy of: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org

Original Distribution of the redbay ambrosia beetle (Xyloborus glabratus)

Port of entry

Origin

Entry into the U.S.

• Redbay ambrosia beetle first detected in Port Wentworth, Georgia in 2002 and by 2003 this beetle and its associated fungus (Laurel Wilt; Raffaelea laurelensis) had caused substantial destruction to the native redbay (Persea borbonia) in Georgia and South Carolina.

• During the spring of 2005 this pest was detected on redbay in Duval County, Florida.

• Since that time the pest has spread southward from northeast Florida (Duval County) along the east coast to as far south as Indian River County.

Entry into the U.S.

• The range of redbay trees is quite extensive (all along the coastal states from Virginia on the east coast to Washington on the west coast) but in the eastern U.S. it extends from Virginia in the north to extreme south Florida.

• There is a danger that this will facilitate the natural spread of the redbay ambrosia beetle and laurel wilt fungus to the commercial avocado production area in Miami-Dade County.

• In addition, avocado trees are planted in home landscapes throughout the state of Florida.

Natural range of redbay in the U.S.(from E.F. Gilman and D.G. Watson)

Current distribution of the pest

• Current distribution of the redbay ambrosia beetle-laurel wilt fungus is in Georgia, South Carolina and Florida.

• Note the pest skipped over several counties. This indicates infested redbay wood was moved from the infested area to the north to the south counties.

Symptoms of redbay ambrosia beetle infestation

• The beetle bores through the bark into the sapwood of the limbs and tree trunks. The beetle may also bore into smaller stems.

• The compacted sawdust (called a string) from the beetle boring into the wood is a common symptom but may not always be present.

Photographs courtesy of: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org and J. Johnson, Georgia Forestry Commission, Bugwood org.

Redbay ambrosia beetle and laurel wilt fungus

• The redbay ambrosia beetle bores into the wood just below the bark of trees, forms galleries in the sapwood, and inoculates these galleries with spores of the laurel wilt fungus.

• The fungus feeds on the sapwood and then the adult and larval redbay ambrosia beetles feed on the fungus.

Infested redbay tree. Note bore wholescaused by the beetle.

Photographs courtesy of: Michael C. Thomas, Florida Department of Agriculture and Consumer Services, Bugwood.org

Infested redbay tree. Note darkstaining caused by the fungus.

Redbay ambrosia beetle and laurel wilt fungus

Exuding sap from avocado stembored into by redbay ambrosia beetle.

Close-up of exuding sap from avocadocaused by the redbay ambrosia beetle boring.

Dark streaking cause by the laurelwilt fungus infection on avocado.Photographs courtesy of Jorgé Peña, UF-IFAS-TREC

Note – These are experimental avocado trees in quarantine.

Entrancehole

Symptoms of the laurel wilt fungus on young avocado trees 20 days after

inoculation with the fungus

Photographs courtesy of Randy Ploetz, UF-IFAS-TRECNote – These are experimental avocado trees in a quarantine setting.

Known host plants

Common name Scientific name

Avocado Persea americana

Camphor Cinnamomum camphora

Pondberry Lindera melissifolia

Pondspice Litsea aestivalis

Redbay Persea borbonia

Sassafras Sassafras albidum

Swampbay Persea palustris

What can you do?

• Redbay and other host forest wood species should not be moved or sold as firewood, tree trimmings, BBQ smoke-wood or mulch.

• Urban and rural residents and commercial growers should be on the look-out for redbay and other host trees (including avocado) showing signs of rapid wilting, dieback, and insect boring and report this to the Dept. of Plant Industry (http://www.doacs.state.fl.us/pi/index.html) and/or your local Cooperative Extension Agent (http://solutionsforyourlife.com).

• This will help regulatory agencies and scientists track the movement of this pest. Preliminarily, redbay ambrosia beetle sightings appear to be highest from July through September.

What can you do?

• Extreme caution should be used in moving avocado trees and wood products into Miami-Dade County from other counties.

• Insect and disease-free containerized avocado trees should only be purchased from reputable nurseries’ and trees showing any signs of wilt or dieback should be destroyed immediately.

Further information

• Please consult EDIS (http://edis.ifas.ufl.edu) for the new factsheets on this pest.

• Florida Dept. of Agriculture and Consumer Services, Dept. of Plant Industry (http://www.doacs.state.fl.us/pi/enpp/pathology/ laurel_wilt_disease.html).

• Forest Management. Fla. Dept. Agri. and Consumer Services, Div. of Forestry. (http://www.fl-dof.com/forest_management/fh_insects_redbay_ambrosiabeetle.html).

• USDA Forest Service. Forest Health Protection, Southern Region. (http://www.fs.fed.us/r8/foresthealth/ laurelwilt/insect_vector.shtml).